function checkemail() {
        var check;
        var email = document.getElementById("email").value;
        var pattern = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;
        if(!pattern.test(email)){
            document.getElementById("emailInfo").innerHTML = "请输入正确的邮箱地址";
            check = false;

            }

        else {
            check = true;
            document.getElementById("emailInfo").innerHTML = "";
        }
        return check;
    }